1. Field of the Invention
The present invention relates to an automatic document feeding apparatus, an image scanning apparatus, and an image forming system. More particularly, the present invention relates to an automatic document feeding apparatus including a function for determining the presence of a document, an image scanning apparatus including such an automatic document feeding apparatus, and an image forming system including the image scanning apparatus and an image forming apparatus.
2. Description of the Related Art
As an example of such a technology, the invention disclosed in Japanese Patent Application Laid-open No. 2006-052082 is known. A document scanning apparatus according to this invention includes a document table on which a plurality of document sheets are placed, a separating unit that separates a document sheet one by one from the document sheets placed on the document table, a paper feeding unit that feeds the document sheet separated by the separating unit to a predetermined position, a last document detecting sensor that detects the last document sheet on the document table, and a document set detecting sensor that detects that a document sheet is placed on the document table. In such a document feeding apparatus, the document sheet is fed while receiving signals from the document set sensor and the last document detecting sensor. When the last document detecting sensor detects that no document sheet is placed on the document table, a feed controller determines whether the document sheet is the last document sheet based on an output from the document set sensor, and outputs a result of the determination.
The invention disclosed in Japanese Patent Application Laid-open No. 2006-052082 is intended to prevent an error in determination of whether a document sheet is the last document sheet without increasing the size of the machine. However, in order to prevent an error in determination of whether a document sheet is the last document sheet, the feed controller needs to perform determination of whether the next document sheet is present four times at most. The number of processes thus increases, resulting in reduced efficiency. Furthermore, because the feed controller determines whether the document sheet is the last document sheet based on an output from the document set sensor when the last document detecting sensor detects that no document sheet is on the document table, the document might not be detected correctly depending on how the document sheet is curled or due to document slipping. Furthermore, when the size of the document sheet is small, the feed controller cannot come to a conclusion as to whether the next document sheet is present based on the outputs from the sensors on the document tray, and can only arrive at the conclusion based on the output from the document set sensor. Therefore, productivity is reduced significantly.
Therefore, there is a need for an automatic document feeding apparatus, an image scanning apparatus, and an image forming system capable of efficiently determining the presence of the next document sheet even when the size of the document sheet is small, without being affected by how the document sheet is curled, document slipping, or the like.